Frequently in the Beethoven violin sonata I'm playing, Beethoven marks a p on the downbeat of a measure following a f passage, even though the passage itself ends on the downbeat. (see p. 3 (as labelled in the score), system 3, ms. 5-6 for an example; see also p. 22, system 3, ms. 2 & 6 )

Is the first beat of the measure really supposed to be a subito piano, or does the new dynamic start on the notes following it? I feel it's kind of anticlimactic (and difficult) to do it on the downbeat.

Are you playing out of an Urtext? If it's like that in an Urtext edition (if you wanna be really sure, see if you can find his manuscript scanned online!!), I assume you should do it exactly how it's written.

It's like that in Henle, so I then went and checked the "first edition" on imslp and it looked like that in the score. I didn't know if that was a thing Beethoven always did, and it's "common knowledge" to play it differently.

I think that's a pretty common Beethoven thing...

Yep. Gotta do the p.

I love that sonata, though. Lots of fun, but a lot harder than people think.

I agree with everybody that indeed it's a "p," right there.

But I think there's a different legitimate question: Can there be some kind of diminuendo leading up to it, like at the very end?

Most would probably say no, but IMO it's not out of the question; the absence of a diminuendo indication doesn't mean you can't do it. I did play the piece, a long time ago, and it's possible that the violinist and I did do it.
I don't think I'd do it now, but I wouldn't rule out trying it both ways and seeing. And BTW, in such a situation, even if I wound up preferring it with the diminuendo, if the violinist said no, I'd relent very easily, and probably with a mock apology for having even thought of it.

I've played it a couple of times, and my recollection is that at the brisk tempo of the piece, a slight diminuendo before the p still creates the impression of a subito p and eases its execution.

An alternate way, without the diminuendo, is to put your bodies into sudden intense spasm for a split second before the p.

Victor Borge or Peter Schickele would have had a good time demonstrating it....

OK, I guess that's enough votes for the p. I'll keep trying, with a diminuendo. Right now I'm cursing the left hand part in the 3rd movement. It's just not possible to get it up to tempo. Actually all the tricky spots in the movement I can sometimes to flawlessly, and other times I get completely stuck and have no idea why it's not working. Sigh. Inconsistency.

MarkC - my body is already locked up before I hit the p, there's nothing else to spasm!

Even though the decision has been made already, I'm still going to solidify it and throw in another vote for the p...

Arghhh!

Orange Soda King!

You have to practice lifting on the C#.

And at some point, you're going to have to go back and learn Clementi or Mozart and figure out how to play scales and passagework with traditional elegant, classical phrasing. (That's what's fussy about this Beethoven sonata, it's not vigorously romantic extreme Beethoven, it's elegant classical Beethoven with a few surprises here and there.)

As for the last movement, the most important marking in the score is leggiermente. If you only observe one marking. let it be that one.

Also, practice those tricky LH bits (like in measure 13) by leaving out the middle note and focusing on keeping the thumb light. Learn the same fingering pattern in the RH on a G major triad, then practice both hands together as a mirror image - let your RH teach your LH how to do it.

And remember - at this point, Beethoven's violin sonatas are very much duo sonatas. The piano part is every bit as difficult as the violin part, if not more difficult. (And what's worse, there's a minimum speed at which a violinist can achieve the right bow-stroke for the last movement. If this were a solo sonata, you could just take a slower tempo, but alas, those darn violin bows!)

Ok, now this made me laugh

Thanks Kreisler for the additional tips. Hopefully they can help me get through the recital next Saturday. Also, on the title page of the first edition in IMSLP, the sonata is called a piano sonata with violin accompaniment.